"If you will accept a little oversimplification, the last decade or so of
global equity market performance can be summarized as follows. U.S.
stocks have profoundly outperformed stocks in the rest of the world,
whether other developed markets or emerging markets.

This outperformance
has been partially driven by U.S. P/E ratios expanding more than in
other markets. But the largest driver of the outperformance has been the
massive superiority of earnings growth in the U.S. relative to anywhere
else. This superior earnings growth has been driven not so much by
strong top-line growth, but by expanding profitability by U.S. companies
relative to sales, gross profits, or other measures that can plausibly
be used as proxies for economic capital."